1. Field of the Invention
The present invention relates in general to a tool holder suitable for use on a machine tool, and more particularly to such a tool holder which is capable of monitoring tool service time.
2. Description of the Prior Art
Generally, a machine tool referred to as a machining center stores a large number of tools in the magazine and transfers a desired tool to the spindle selectively during the machining operation so as to carry out various machining operations with a single machine tool. In such machine tool, the number of the tools controlled in a single machine tool increases as the machining operations become more complex.
In addition, it is necessary to attach a different identification number to each tool and to read out the identification number so as to select a desired tool automatically. Furthermore, it is necessary to monitor the actual service time and lifetime of each tool because each tool has a limit as to service time due to wear of the tool.
For detecting the identification number and the lifetime from the tool holder, a memory device for storing the identification number and the lifetime can be provided on the tool holder.
On the other hand, the service time of each tool is cumulatively counted by a CPU in a numerical control apparatus. Namely, when one tool is selected, the CPU reads out the present service time from the memory device in the numerical control apparatus and counts or records the time during which a machining operation with a selected tool is carried out according to the machining command in a numerical control program. Thereafter, the CPU adds the counted or recorded time to the readout of service time and stores the renewed service time into the memory in the numerical control apparatus.
In the above described control apparatus, the burden of the CPU in the numerical control apparatus becomes relatively large because of the calculation of the service time.
It is also necessary to store a complex software program for monitoring the service time in the numerical control apparatus.
Moreover, it is difficult to monitor the service time of each tool in the machine tool, which is not provided with the numerical control apparatus, because the monitoring process of the service time is executed by the software program stored in the numerical control apparatus.